Front Sight Gas Block Issue

[croue]

Hello,

I'm generally only in the reloading forum, but have a question that definitely doesn't belong there. Hoping I can find some advice here.

I've been having issues with an upper I built a while back. My first and only upper so far. I was having feeding issues that seemed to best match a lack of adequate gas. (Carbine length gas system on 16" barrel) that I mostly resolved by realigning the front gas block very carefully (circumferentially) and sealing things with loctite a bit.
But I was still having trouble with failure to feed on some of my reloads, but not nearly as often on factory 5.56 rounds. (higher pressure helps probably?) Chased my reload recipe and quality for a bit, but I don't think it's there. I have tried them in other uppers with no issues at all. The problem seems to be with my specific build still. (I know, no surprise there! )

Took the barrel assembly apart all the way to check things out and discovered when I mic'd everything that the front sight gas hole was about a half hole or so off from aligning longitudinally with the barrel gas hole. Exactly the thickness of the front foreend cap as it happens. Without the cap, it aligns perfectly (obviously not a solution though). But the shoulder on the barrel keeps me from aligning it better by sliding it proximally. I also see a telltale black spot on the barrel (ss barrel) that tells me where the front sight gas hole is aligned on the barrel.

I presume this is more than enough to cause issues. Correct me if that assumption is wrong.

I think I have a few choices. Change barrel or block is one. Not attractive, and not sure if a new gas block won't have the same issue. Machining barrel or block to by 0.035" - but I don't have access to a lathe, and the block would need reanodizing.

But I was thinking about also relieving the opening of the gas port in the front sight block by drilling the opening oversize by the 0.035" to make it line up. i.e. Just drill the opening over size to about 0.100" or so deep leaving a drill point taper. The gas shouldn't care to much about that little cavity and can then find it's way into the gas tube quite nicely without as much loss at the 'half-hole'.

Is this a bad idea?

C

[croue]

FWIW I'll add the measurements - the gas hole is 0.275" from the rear of the front sight gas block.
The gas hole is also 0.275" from the shoulder on the barrel.

There isn't proper allowance for the 0.035" thick cap. The hole should be only 0.240" from the rear of the front sight block for proper alignment.

C

[buellster]

If it were me, I would machine the block 0.035". But drilling out the port in the block to match up with the barrel port shouldn't adversely affect function.

[kcstott]

with the tools you have drill the block but you'll need to drill it .070" over size to get .035" on one side.

[d.f.anonymous]

Another approach, if I might offer, is around about $100, is an adjustable gas block. https://youtu.be/evnB_C3U-Uc

[d.f.anonymous]

But its more than likely the alignment is the issue, try using a gas block alignment tool, or use an air compressor, or do what I do and use a white out pen and draw measurements and alignment doodles all over the barrel to get alignment and scrub it off.